This invention relates to a control device for controlling oscillation on a mold in a continuous casting machine.
Continuous casting process has been used for manufacturing slabs or billets from molten metal. For this purpose, the molten metal is first poured into a mold. The molten metal is covered with powder (lubricant) being sifted on the surface thereof. The mold is then cooled to quench the molten metal, which in turn is further cooled at a guide roll assembly. The metal solidifies completely at the guide roll assembly and drawn through pinch rolls. The molten metal in the mold is moved downward along the inner surface thereof as the solid metal is drawn off the casting station. In this event, the powder contributes to inhibiting air oxidation of the metal and trapping inclusions on the metal surface. The powder lies between the mold and the molten metal, which improves lubrication of their interface. It also prevents the molten metal in the mold from being quenched excessively. The mold is shaken up and down repeatedly to reduce the damage on the inner surface of the mold caused by the direct contact with the metal. Though this vertical shaking is helpful for reducing the damage of the mold, it is not enough for effective inflow of the powder. Poor inflow of the powder badly affects the quality of end products and sometimes results in the sticking of the molten metal in the inner surface of the mold. This may cause a breakout of the mold as well as the molten loss hindering the effective casting of the metal.
To overcome the above mentioned problem, the present inventors have been developed a device for moving a mold while shaking the entire structure of the mold up and down. The mold comprises two long-side plates opposed to and in parallel with each other. The mold also comprises two short-side plates opposed to and in parallel with each other. The long-side and short-side plates construct the mold, which is surrounded by a rectangular mold frame with some distance away. As well known in the art, the long-side plates move closer to and away from each other in synchronism with the vertical movement of the mold. The long-side plates are in the most close relation when they contact with the short-side plates. When the long-side plates are extremely distant, there is the largest space between the mold and the molten metal. The problem of poor inflow of the powder can thus be solved by means of moving the long-side plates quickly.
The expansion and contraction of the short-side plates are, however, ignored in the above mentioned device. In other words, the short-side plates are regarded to be constant in width though they expand and contract over the temperature difference. The extent of expansion and contraction depends on heat transferred from the molten metal, which affects the distance between the long-side and the short-side plates. Expansion of the short-side plates results in the smaller distance between the long-side and short-side plates. This reduces the distance for moving the long-side plates and thus the space between the long-side plates and the molten metal. The smaller space can receive less powder, which badly affects the quality of end products. As mentioned above, poor inflow of the powder may be a cause of the sticking type, the breakout and the molten loss of the mold. On the contrary, contraction of the short-side plates increases the distance between the long-side and short-side plates. This may also cause the breakout due to the infiltration of the molten metal into the above mentioned gap.
As mentioned above, these plates should be held such that a suitable distance can be obtained between the long-side and short-side plates. For this purpose, a sensor can be used for sensing the thermal expansion of the short-side plates to adjust the distance between the long-side and short-side plates. The sensor of this type is useful only when the thermal expansion on each component is quite equal in the mold. Thus it is usually impossible to determine positively the thermal expansion on various components of the mold.